M Farooq,
M A Mian, F R Durrani and M
Syed

Abstract

This
study was carried out during the years 2000-2001 in 109 flocks to investigate
prevalent diseases and mortality in egg type layers in Chakwal
district. Mortality was defined as the sum of culled and dead birds during a 52
week period prior to disposal of the flock.

Overall mortality due to
various anomalies was 6.67% and there was no known etiology for around 2% of
the losses. 2.74% of birds were culled over the whole period. Diseases caused
higher mortality during brooding (50.4%) and laying (31.3%) than during growing
(18.3%). Coccidiosis was the major problem causing
19.1% mortality with higher incidence during brooding and in birds kept on the
floor. Egg prolapse
and enteritis resulted in 12.1% and 8.4% mortality, respectively. About 7% of
loss was due to disease outbreaks including E.
coli, Infectious Coryza and Chronic Respiratory
disease (CRD). Losses due to Infectious Bronchitis (IB), Omphalitis,
yolk sac infection, ascities and feed toxicity in
each case were around 6%, while Hydro-pericardium syndrome and cannibalism
caused below 5% losses. Overall mortality was 11.4±1.14% with a coefficient of variation of 108%,
representing a relative percent mortality rate of 31.4±0.46, 25.5±0.53
and 43.2±0.49 during brooding, growing and laying periods, respectively.
Hygienic condition, housing system, cage vs. floor rearing, strain of the
chicken and flock size affected mortality in egg type layers. Mortality was found negatively correlated with peak lay (r= -0.43; p<0.001), percent lay (r=
-0.29; p<0.002), hen-day egg
production (r= -0.25; p<0.017) and net profit per bird (r= -0.68; p<0.001) but positively correlated
with age at first lay (r= 0.19
p<0.04). Higher mortality at any stage was observed in small sized flocks,
overcrowded houses and birds maintained under poor hygienic conditions.
Mortality during lay was also higher in birds kept on the floor than those in
cages.

Avoiding
overcrowding, effective use ofbrood-grow house under better hygiene, appropriate light schedule and
use of cages instead of floor houses for egg type layers will reduce mortality.

Introduction

Mortality plays a major role in
determining profit from egg type layers and is a function of dead and culled
birds over the growth and production period.A negative association of mortality with net profit in chicken
production has been reported by Farooq et al (2001), Zaheer-ud-Din et al (2001) and Asghar
et al (2000). Kitsopanidis and Manos (1991) also reported a reduction in
net profit when mortality was more than 2-5%,whereas North (1984) reported poor economic performance of egg
type layers at mortality level of more than 10%. Chew (1983) reported a mortality in layers ranging from
3.1 to 18%. Mortality in egg type chicken at any stage of life will affect
performance of egg type layers; however, higher mortality during the laying
period will badly affect productivity. Ghodasara et
al (1992) reported relatively higher mortality rate during laying (49%) than
during the brooding (26%) and growing period (24%), resulting in poor
performance.

Possible causes of higher mortality
in egg type layers could be severe out breaks of infectious and non-infectious
diseases, accidental deaths, substandard hygiene/management conditions, poor
quality chicks/feed and egg prolapses. A higher incidence of Salmonellosis
was found in flocks maintained under poor management conditions (Majid et al 1991). The most prevalent diseases
resulting in higher mortality in egg type layers were Infectious Bronchitis
(90% mortality; Rikula et al 1993), Infectious Bursal disease (40.4%, Anjum et
al 1993), Newcastle disease (51.5%, Amin et al 1995),
Coccidiosis and yolk sac infection (35.2 and 31.4%,
respectively; Ghodasara et al 1992). According to
North (1984), coccidiosis was more detrimental beyond
the age of 20 weeks as it adversely affected egg production performance of egg
type layers. The author stated that layers should develop full immunity against
coccidiosis before the egg production process is
initiated as coccidiosats are not added in the layer
ration and an incidence of coccidiosis during the
laying period would therefore result in poor egg production. Egg prolapse was
one of the serious problems reported to cause 9.4% mortality in egg type layers
(Tablante et al 1994). Besides its direct
contribution to mortality, it usually leads to cannibalism in the flock causing
additional loss.

Age of the chicken and onset of
seasonal and climatic conditions could also play a major role in prevalence of
the diseases. Birds vaccinated against IBD before the 10th day-age were more
affected than others (Anjum et al 1993). Singh et al
(1994) reported higher prevalence of IBD, Coccidiosis,
E. coli and other bacterial
infections in between the age of 6 and11 weeks, than at the age of 18 to 22
weeks. Assurance of a healthy environment (Khurshid et al 1995), effective vaccination against
diseases, antibiotic therapy, maintenance of healthy environment and protection
of birds from extreme climatic conditions could reduce incidence of mortality
many folds according to Mukherjee and Khamapurkar (1994).

The present
study was an effort to investigate prevalent diseases and mortality in egg type
layers at various stages of life and suggest effective strategies to minimize
mortality.

Materials and methods

Data source and prediction
of sample size

The present
study was carried out during the years 2000-2001 to investigate mortality and
prevalent diseases in egg type layers in Chakwal, Punjab, Pakistan.Sample size for the study was predicted by
calculating the coefficient of variation from the data generated in the same
area by Tariq et al (2000). Maximum coefficient of
variation was found for total number of eggs produced/flock and was selected as
an index for predicting sample size to accommodate both maximum and minimum
values of variations in other production and economic traits. The following
model, developed by Casely
and Kumar (1989), was adopted for determining sample

K2 * V2

N =-----------

D2

Where “N” was
sample size, “K” the normal deviation at 95% confidence interval, “V” the
coefficient of variation of the selected variable and“D” the margin of error assumed to be 0.1.

Data collection

After
predicting the required sample size, data from 109 flocks regarding shed
capacity, flock size, strain of the chicken, mortality, culling, causes of
mortality, system of housing, rearing facility (cage vs. floor), hygienic
measures adopted, vaccination practice, egg production traits, cost of
production and returns were collected. The hygienic status of the farm
was categorized as good, average and poor on the basis of floor and
house construction, vicinity of the farm, distance between sheds or other
dwellings, house conditions, “all in… all out” system, cleanliness and sanitation
of equipments/houses and disinfecting procedures adopted. All the farmers were
following a standard vaccination/debeaking program
advised by the chick suppliers.Density
of layers in a shed was assessed on the basis of number of chicks or birds/m2.
Deviation above or below the recommended level was grouped as over or under
utilization of the available space.

Data analysis

Weighted means or averages

To account
for the wide variability in flock size, weighted means were calculated instead
of simple averages, using the following equation;

SWiXi

X
=----------------------

SWi

Where“X “ was the weighted mean, “Xi “ the
variable, “Wi” the weight factor / number for a
particular variable. The effect of density of birds/m2 area in the
shed, hygienic condition on the farm, strain of chicken, flock size, cage vs.
floor rearing and system of housing on overall mortality in egg type layers
maintained was studied adopting the procedure of Steel and Torrie(1981). The following statistical model was constructed to ascertain the
effect of aforementioned model on overall mortality;

Yijklmno
= µ + ai + bj
+ ck + dl+em+ fn+ (axb)ij+gijklmno

Where “Yijklmno“ was the response variable (overall
mortality in egg type layers),“µ” the
population constant common to all observations, “ai“
the effect of i-th hygienic condition of the farm (i= poor, average and good), “bj“
the effect of j-thfdensity
of birds/m2 (j= over utilized, optimally utilized and under
utilized),“ck“ the effect of
k-th housing system (k = brood-grow-lay house,
brood-grow house and grow -lay house), “dl” the effect of l-th housing facility (l= cage vs. floor rearing), “em” the effect of m-th
flock size (m= small; <1000, medium; >10000<20000 and
large; >20000), “fn” the effect of n-th
strain of the chicken (n= Babcock, Nick-chick, Hyline
and Hisex), “(axb)ij“ the interaction between i-th
hygienic condition and j-th density of birds/m2
and “gijklmno” the residual term
associated with each Yijklmno, normally,
independently and identically distributed with mean zero and unit variance.

Pearson's
correlations between mortality, age at first lay, peak lay, percent lay,hen-day egg production, egg laying period, cost of production,
therapeutic cost and net profit per bird were worked out using the
following formula,

rX,Y=Cov (X,Y)

óxóy

Results and discussion

Prevalent diseases in egg type layers

Necropsyrecords maintained on the farms were
scrutinized to investigate prevalent diseases. Overall mortality due to various
anomalies was 6.67%. No necropsies’ records were available for around 2%
losses. Total mortality due to various anomalies revealed higher prevalence of
diseases during brooding (50.4%) and laying (31.3%) than during growing
(18.3%). Coccidiosis was found as a major problem. Ghodasara et al (1992) reported higher incidence of coccidiosis (35.3%) than the present findings (23.4%).
Relative rate of coccidiosis among layers in Chakwal revealed higher mortality during brooding than
during laying. The higher incidence of coccidiosis
than any other disease in the present findings may be attributed to poor
hygienic conditions on the farms coupled with poor management

Table 1.
Losses due to various diseases in egg type layers in Chakwal

Disease

Brooding

Growing

Laying

Overall

InfectiousCoryza

10.05±0.78

7.65±0.23

10.05±0.12

9.25c±0.31

Chronicrespiratorydisease

7.42±2.10

5.71±2.03

12.85±2.19

8.66c±2.33

InfectiousBronchitis

10.13±2.71

6.51±2.13

2.41±1.39

6.35d±3.18

InfectiousBursaldisease

5.35±1.89

3.44101.78

6.12±2.02

4.97e±2.91

Hydro‑pericardiumsyndrome

4.32±0.98

1.44±0.89

6.72±2.33

4.32e±0.99

Newcastledisease

5.10±1.02

3.13±1.11

1.85±1.23

3.36e±1.13

Coccidiosis

28.44±0.23

19.87±0.47

21.97±0.08

23.43a±0.12

Escherichiacoli

12.44±2.95

8.60±3.12

8.56±0.93

9.87c±3.23

Toxicity

11.56±2.11

5.25±2.11

12.60±1.33

9.79c±2.21

Enteritis

10.97±0.57

8.78±0.56

6.59±0.28

8.77c±0.37

Omphalitis

6.29±0.34

0

0

6.29d±0.29

Yolksacinfection

5.36±0.73

0

0

5.36de±0.11

Ascities

19.72±0.09

2.9±0.33

0

7.54bc±0.19

Eggprolapse

0

0

15.20±3.17

15.20b±3.17

Cannibalism

4.69±0.45

2.34±0.89

6.82±0.45

4.62e±0.32

abcd Means with different
subscripts are significantly different ata =0.05

Egg prolapse was the second most prevalent problem. Tablante et al (1994) reported lower mortality (9.4%) due
to egg prolapse than the present findings. Enteritis
was another major problem in the present study.Farooq et al (2001) reported an almost similar
incidence of CRD, Coryza and E. coli but higher incidence of IBD in egg type layers among the
cases submitted to the Poultry Research Institute in Chakwal.
Higher losses due to IBD have also been reported by Rikula
et al (1993) and Amin et al (1995) compared with the
present findings. In the current study, thedata on the prevalent diseases which revealed lower incidence of
infectious diseases like ND and IBD indicate the effective role of vaccination
for infectious diseases and the need for good hygiene and management
conditions.

Mortality
and management

Overall mortality was higher in Hyline and Hisex strains thanin Babcock and Nick-chick (Table 2).Petek (1999) and Tolimir and Masic (2000) also
reported differences in mortality among various strains of egg type birds.

Table 2. Mortality in egg type
layers as affected by strain of the chicken

Babcock

Nick-chick

Hyline

Hisex

Mortality (%)

Brooding

3.12c±0.29

4.00b±1.55

3.50c±0.89

4.64a±1.62

Growing

3.40b±0.50

3.75b±0.9

4.95a±2.01

3.70b±2.01

Laying

3.01c±0.45

3.20c±0.7

4.63a±1.74

3.85b±0.7

Overall

9.53c±0.91

10.9b±2.9

13.0a±3.67

12.2a±2.6

abcMeans with different
subscripts are significantly different ata =0.05

Mortality
was higher in small than in large sized flocks (Table 3). Verma
and Singh (1997) and Farooq et al (2000) also
reported higher mortality in small than in large sized flocks. The findings of
the present study suggest that flock owners maintaining a larger flock size
would have ensured better utilization of inputs and available resources to
avoid undue risks of mortality.

Table 3. Mortality in egg type layers
as affected by flock size

Small

(<10,000)

Medium

(>10,000<20,000)

Large
(>20,000)

Mortality (%)

Brooding

4.40a±0.71

3.00b±0.31

2.22c±0.29

Growing

4.26b±0.48

5.31a±2.31

3.28c±0.29

Laying

4.98a±0.45

3.44b±1.96

3.43b±0.15

Overall

13.6a±1.20

11.7b±4.20

8.93c±0.39

abcMeans with different subscripts are
significantly different ata =0.05

Mortality was higher in flocks produced
in brood-grow-lay houses than in those produced in brood-grow and lay houses
(Table 4).

Table 4. Mortality in egg type
layers as affected by housing system

Brood-grow-lay

Brood-growandlay

Broodandgrow-lay

Mortality (%)

Brooding

5.57a±1.6

2.89b±0.24

2.98b±0.34

Growing

4.50a±0.9

2.40c±0.15

3.84b±1.13

Laying

4.85a±0.84

2.79b±0.17

4.50a±0.95

Overall

14.9a±2.36

8.08c±0.45

11.3b±2.01

abcMeans with different
subscripts are significantly different ata =0.05

Mortality rate was highest in
over-crowded houses and lowest in house with the optimum bird density (Table
5).

Table 5.Mortality in egg type layers as affected by
bird density

Optimum

Under

Over

Mortality (%)

Brooding

2.09c±0.56

4.02b±0.49

5.35a±1.56

Growing

2.01c±0.31

3.11b±0.48

3.84a±2.03

Laying

3.77b±0.44

3.04c±0.47

5.92a±1.65

Overall

7.77c±1.03

10.2b±1.05

15.1a±3.88

abcMeans with different
subscripts are significantly different ata =0.05

Table 6.Mortality in egg type layers
as affected by hygienic conditions on the farm

Poor

Average

Good

Mortality (%)

Brooding

4.73a±1.03

3.51b±0.56

3.35b±0.26

Growing

4.49a±1.22

3.10b±0.30

2.94b±0.16

Laying

5.25a±0.96

3.63b±0.27

3.32b±0.14

Overall

14.4a±1.03

10.2b±0.68

9.61b±0.42

abcMeans with different
subscripts are significantly different ata =0.05

Lower mortality was found among flocks reared in cages than in those
kept on the floor (Table 7).Horne-Van and Van-Horne (1994) and North
(1984) also reported higher mortality in flocks kept on the floor than those
kept in cages. This can be attributed to
poor litter management and greater disease risk. Coccidiosis
during the laying period was higher in birds kept on the floor than in
cages.

Table 7.Mortality in egg type layers reared on the
floor or kept in cages

Cage

Floor

Mortalityduringlaying
(%)

2.29b±0.16

7.57a±0.95

abMeans with different
subscripts are significantly different ata =0.05

Mortality was negatively correlated with peak lay (r
= -0.43), percent lay
(r = -0.29), hen-day egg production (r = -0.24) and net profit per bird (r
= -0.68)
but tended to be positively correlated with age at first lay (r= 0.19). The findings suggested that
increased rate of mortality delayed age at first lay and resulted in a decrease
in egg production performance and profit.

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